The present application is directed toward improvements in anti-lock systems such as those described in U.S. Pat. Nos. 3,966,267 and 3,929,382, assigned to the assignee of the present invention.
In general, prior wheel lock control systems, such as those immediately above-referenced, have provided a lock signal, for releasing the braking forces on the wheels of the vehicle, under particular wheel operating conditions, all for the basic purpose of systems of this general type, namely minimization of wheel locking due to braking.
In general, a system of the kind aforementioned has provided deceleration detection circuitry for sensing when the speed of a braked wheel decreases at a rate substantially faster than obtainable by a vehicle, indicating an impending wheel lock condition, for releasing the braking force until such wheel deceleration ends and thereafter permitting braking force to be restored to continue slowing the vehicle.
The aforementioned apparatus also includes fixed bleed circuitry for providing a skid signal when the average wheel speed of the two wheels being monitored decreases below a declining reference signal representative of a desired rate of decline in the speed of the faster wheel. This circuit is useful under light load and/or low coefficient friction conditions, wherein a wheel may lock very rapidly, before the deceleration logic lock signal has had an opportunity to exhaust the brakes sufficiently to allow the wheels to spin up toward vehicle speed. Once the wheel has stopped in the locked condition, it is of course no longer decelerating and thus no longer causing the deceleration logic to provide a lock signal. The fixed bleed logic overcomes this problem by furnishing its own lock signal well before the rapidly decelerating wheel locks, signaling the brakes to keep exhausting. The fixed bleed circuit terminates its lock signal when such wheel has spun up to a speed corresponding to a desired fraction of the vehicle speed, as the latter is simulated by a portion of the fixed bleed circuitry.
The aforementioned prior lock control systems also provide differential wheel speed logic to produce a lock signal where speeds of the two wheels being monitored substantially differ as may result, for example, from a split coefficient of friction between the road surface and each of the two wheels. When the wheel speed difference becomes too great it is desirable to release the brake forces to prevent lockup of the lower speed wheel.
The aforementioned prior systems, and predecessors thereto, have in some instances included additional functions. For example, the system of aforementioned U.S. Pat. No. 3,929,382 incorporated delay circuitry to delay the application of signals from one of the circuits above-mentioned to the braking system, as well as acceleration circuitry responsive to spin up acceleration of a wheel following the initiation of brake release. One of the aforementioned systems has provided for monitoring of some circuits therein and for blocking of a lock signal should a monitored circuit develop a specific fault.
Systems constructed in accord with aforementioned U.S. Pat. Nos. 3,929,382 and 3,966,267 have enjoyed commercial success and have been generally satisfactory. However, a continuing effort to perfect systems of this kind has led to the present invention.
Accordingly the objects of this invention include provision of:
A lock control system capable of performing substantially the functions aforementioned with simplified circuitry and being capable of performing additional functions with little additional circuitry or complication.
A system, as aforementioned, in which wheel speed signals applied to deceleration detection, fixed bleed, and other circuitry within the system are related nonlinearly to the speeds of the respective wheels represented thereby, and in which deceleration, fixed bleed, etc. circuitry can accordingly be simplified and made substantially linear in operation, despite the need in such circuits to produce lock signals in nonlinear relation to actual wheel speed, to compensate for the greater MPH change at high speeds than at low speeds resulting from the requirement for a certain constant percentage of slippage at both low and high wheel speeds.
A system, as aforesaid, incorporating nonlinear frequency to voltage convertors to provide nonlinear wheel speed signals.
A system, as aforesaid, including improved deceleration detector and fixed bleed circuitry of simplified and linearized arrangement, including, in the fixed bleed portion, feedback of lock signals to control the input into the fixed bleed circuitry.
A system, as aforesaid, which provides for monitoring of operation of the wheel speed signal generating circuitry, particularly to protect against erroneously high wheel speed signals and which is capable of overruling lock signals under such a fault condition.
A system, as aforesaid, which in one embodiment additionally provides for monitoring of valve driver circuitry disposed between the lock signal generating circuitry and the braking system, particularly for monitoring correspondence of inputs to outputs in such valve driver or circuitry.
Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.